Implantable blood pumps can be utilized for total artificial heart replacement or ventricular assistance. Implantable blood pumps may be utilized for temporary or long term ventricular assistance or to permanently replace a patient's damaged heart. Some blood pumps may mimic the pulsatile flow of the heart. However, some blood pumps have progressed to designs that are non-pulsatile. Non-pulsatile blood pumps are typically rotary and propel fluid with impellers that span the spectrum from radial flow, centrifugal type impellers to axial flow, auger type impellers.
A common issue encountered by blood pumps is blood trauma. The causes of blood trauma can be partially attributed to shear stress and/or heat generated by the bearings supporting the impeller. Shear stress and/or heat may cause hemolysis, thrombosis, and the like. In some blood pumps, the impeller may be driven by a shaft. The shaft may be sealed off with shaft seals to prevent blood from entering undesirable areas, such as a motor driving the shaft. However, shaft seals generate excess heat that may produce blood clots, and shaft seals may fail and allow blood to enter unwanted areas. A great deal of effort has been devoted to reducing or eliminating blood trauma in rotary blood pumps. One solution to minimizing or eliminating blood trauma is to provide hydrodynamic support of the impeller. For example, hydrodynamic support may be provided by ramp, wedge, plain journal, multi-lobe or groove hydrodynamic bearings. Another solution is to provide mechanical support of the impeller using mechanical bearings, such as jewel type bearings in the form of a shaft and sleeve or ball and cup. These mechanical bearings may utilize biocompatible hard ceramic materials. To function properly in blood, a mechanical bearing must generate very little heat and should avoid stagnant or recirculating areas of blood flow to prevent the formation of blood clots. Another solution proposed is the utilization of passive permanent magnetic and active controlled magnetic bearings to provide impeller support in blood pumps. Magnetic bearings, hydrodynamic bearings, and/or mechanical bearings may be combined to provide impeller support in blood pumps. However, magnetic bearing systems may require sensors and complex controls. Hydrodynamic bearings may require small clearances which may cause slow moving or stagnant blood flow between hydrodynamic bearing surfaces. Further, some blood pumps incorporate electric motors into the pumping chamber, rather than providing separate motor and pumping chambers. For example, a stator may be provided in the pump housing and magnets can be incorporated into an impeller to provide a pump impeller that also functions as the rotor of the electric motor.
The various embodiments discussed herein provide mechanical blood pump bearings that cause minimal blood trauma, generate very little heat from friction, and can be thoroughly washed by blood flow to prevent the formation of blood clots. Further, these bearing systems are simple and robust, without requiring complicated controls and sensors or small clearances.